Lubricant supported electric motor with electricalconductors functioning as an outer raceway

ABSTRACT

An electric motor comprises a stator presenting a first surface. A rotor is rotatable relative to the stator. The rotor presents a rotor raceway disposed in spaced relationship with the first surface of the stator. The first surface of the stator defines a plurality of slots in spaced relationship with one another to define a plurality of spaced teeth between the slots. At least one electrical conductor is disposed in each of the slots and configured to selectively create a moving magnetic field for acting upon the rotor for providing rotational movement of the rotor. A portion of the at least one electrical conductor extends substantially into radial alignment with, or past the first surface of the stator to at least partially define a stator raceway of the stator for engaging the rotor raceway of the rotor during relative radial movement between the rotor and the stator.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/341,673, filed on Jun. 8, 2021, which claims priority to U.S.Provisional Patent Application Ser. No. 63/036,167, filed Jun. 8, 2020,the entire disclosure of which is hereby incorporated by reference inits entirety.

TECHNICAL FIELD

The present disclosure relates generally to a lubricant supportedelectric motor. More specifically, the present disclosure relates to alubricant supported electric motor with a raceway of a stator defined byelectrical conductors.

BACKGROUND

This section provides a general summary of background information andthe comments and examples provided in this section are not necessarilyprior art to the present disclosure.

Various drivelines in automotive, truck, and certain off-highwayapplications take power from a central prime mover such as an internalcombustion engine (“ICE”) and distribute the power to wheels usingmechanical devices such as transmissions, transaxles, propeller shafts,and live axles. However, attention is being increasingly directedtowards alternative arrangements of prime movers that provide improvedenvironmental performance, eliminate mechanical driveline components,and result in lighter-weight vehicles with more space for passengers andpayload.

“On wheel”, “in-wheel” or “near-wheel” motor configurations are onealternative arrangement to traditional ICE prime movers that distributethe prime mover function to each or some of the plurality of wheels viaone or more motors disposed on, within, or proximate to the plurality ofwheels. For example, in one instance, a traction motor, using a centralshaft through a rotor and rolling element bearings to support the rotor,can be utilized as the “on wheel”, “in wheel” or “near wheel” motorconfiguration. In another instance, a lubricant supported electricmotor, such as described in U.S. application Ser. No. 16/144,002, can beutilized as the “on wheel”, “in wheel” or “near wheel” motorconfiguration. While each of these motor configurations result in asmaller size and lighter weight arrangement as compared to the primemovers based on ICEs, there remains room for further improvements.

For example, the utilization of traction motors as the “on wheel”, “inwheel” or “near wheel” configuration still results in motors that arerelatively heavy and often not sufficiently robust for shock loading inorder to be optimized for wheel-end applications. In other words,present traction motors are large, heavy structures supported by rollingelement bearings, which are relatively heavy for practical wheel endapplications. Lubricant supported electric motors as the “on wheel”, “inwheel” or “near wheel” motor in an automotive or land vehicleapplication are a lightweight alternative to traction motors. Suchlubricant supported motors include a lubricant disposed in a gap betweena rotor and stator for supporting the rotor within the stator andproviding continuous contact between these components. The lubricant maytherefore act as a bearing (e.g., suspension) between the rotor andstator, minimizing or preventing contact therebetween. It is known tolocate a bearing sleeve of high resistivity material such as Hastelloyor Delrin between the rotor and stator to accommodate rotational contactbetween the rotor and stator. An issue with such bearing sleeves is thatthey can cause eddy current losses from the stator, thus leading todecreased performance. It is also known to locate a non-conductivepolymer bearing sleeve between the rotor and stator, however suchbearing sleeves have relatively poor mechanical properties. Furthermore,both of these options require additional fabrication and assembly steps.Accordingly, although known lubricant supported electric motors providea lightweight alternative to traction motors, there remains a need forfurther improvements.

SUMMARY OF THE INVENTION

An electric motor comprises a stator presenting a first surface. A rotorextends along an axis and is rotatable relative to the stator. The rotorpresents a rotor raceway disposed in spaced relationship with the firstsurface of the stator to define a gap therebetween for containing alubricant. The first surface of the stator defines a plurality of slotsin spaced relationship with one another to define a plurality of spacedteeth between the slots. At least one electrical conductor is disposedin each of the slots and is configured to selectively create a movingmagnetic field for acting upon the rotor for providing rotationalmovement of the rotor in response to a current being applied to the atleast one electrical conductor. A portion of the at least one electricalconductor in each of the slots extends substantially into radialalignment with, or past the first surface of the stator to at leastpartially define a stator raceway of the stator for engaging the rotorraceway of the rotor during relative radial movement between the rotorand the stator to function as a bearing while also creating the movingmagnetic field.

The use of one or more electrical conductors such as windings (andoptionally also the stator core) to define the outer raceway allows theelectrical conductors to not only provide current conduction to drivethe rotor, but also to mechanically support the stator. This eliminatesthe need for a separate stator bearing sleeve to mechanically supportthe stator, thus providing a more simple and compact assembly andsimplifying manufacturing and assembly of the electric motor.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects of the present disclosure will be readily appreciated, asthe same becomes better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1 is a schematic view of a lubricant supported electric motor;

FIG. 2 is a perspective, cutaway view of the stator of the lubricantsupported electric motor illustrating an inside diameter of the statorcomprised of electrical conductors and teeth of the stator;

FIG. 3 is a perspective view of a rotor of the lubricant supportedelectric motor;

FIG. 4 is a partial, front cross-sectional view of a stator and a rotorof the lubricant supported electric motor illustrating electricalconductors in a slot of the stator which act as an inner raceway; and

FIG. 4A is a partial, front cross-sectional view of a stator of thelubricant supported electric motor illustrating an alternate arrangementof electrical conductors in a slot.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Example embodiments of a lubricant supported electric motor with atleast one electrical conductor that functions as an outer raceway of astator in accordance with the present disclosure will now be more fullydescribed. Each of these example embodiments are provided so that thisdisclosure is thorough and fully conveys the scope of the inventiveconcepts, features and advantages to those skilled in the art. To thisend, numerous specific details are set forth such as examples ofspecific components, devices and mechanisms associated with thelubricant supported electric motor to provide a thorough understandingof each of the embodiments associated with the present disclosure.However, as will be apparent to those skilled in the art, not allspecific details described herein need to be employed, the exampleembodiments may be embodied in many different forms, and thus should notbe construed or interpreted to limit the scope of the disclosure. Thefollowing example embodiment describes a radial flux electric motor 10with a rotor 14 rotatably located within a stator 12. The teachingsherein may also be applied to a reverse radial flux motor with a rotorrotatably positioned about a stator, axial flux motors and axial/radialflux motors without departing from the scope of the subject disclosure

FIGS. 1-4A illustrate a lubricant supported electric motor 10 inaccordance with an aspect of the disclosure. As best illustrated in FIG.1 , the lubricant supported electric motor 10 includes the stator 12 andthe rotor 14 extending along an axis A and rotatably disposed within thestator 12 to define a gap 16 therebetween. A lubricant 18 is disposed inthe gap 16 for supporting the rotor 14 within the stator 12, andproviding continuous contact between these components. The lubricant 18may therefore act as a buffer (e.g., suspension) between the rotor 14and stator 12 to minimize or prevent contact therebetween. In otherwords, the lubricant 18 minimizes direct contact between the stator 12and rotor 14 and provides an electric lubricant supported motor 10 whichis robust to shock and vibration loading due to the presence of thelubricant 18. Additionally or alternatively, a substantiallyincompressible lubricant 18 may be used in order to minimize the gapbetween the stator 12 and rotor 14.

As further illustrated FIG. 1 , the stator 12 defines one or morepassageways 20 in fluid communication with the gap 16 for introducingthe lubricant 18. The passageway 20 may also be provided on any othercomponents of the lubricant supported electric motor 10 withoutdeparting from the subject disclosure. According to an aspect, thelubricant 18 may be cycled or pumped through the passageway 20 and intothe gap 16 in various ways. For example, a high pressure source 21(e.g., a pump, schematically shown) of the lubricant 18 may be fluidlycoupled to a low pressure source 23 (e.g., a sump, schematically shown)of the lubricant 18, and the lubricant may move from the high pressuresource to the lower pressure source 23, through the passageway 20 andinto the gap 16. Furthermore, rotation of the rotor 14 relative to thestator 12 may operate as a self-pump to drive lubricant 18 through thepassageway 20 and into the gap 16.

As further illustrated in FIG. 1 , the rotor 14 is coupled with a driveassembly 22 for coupling the lubricant supported electric motor 10 toone of the plurality of wheels of the vehicle. For example, in oneinstance, the drive assembly 22 may include a planetary gear system.Alternatively, the drive assembly 22 may include one or more parallelaxis gears. The stator 12 and rotor 14 are configured to exert anelectromagnetic force therebetween to convert electrical energy intomechanical energy, moving the rotor 14 and ultimately driving the wheelcoupled to the lubricant supported electric motor 10 via the driveassembly 22. The drive assemblies 20 may provide one or more reductionratios between the lubricant supported electric motor 10 and the wheelin response to movement of the rotor 14.

With reference to FIGS. 1, 2, 4 and 4A, the stator 12 includes a core 23that is comprised of a plurality of axially compressed laminations 25 ofa steel material (schematically shown in FIG. 1 ). The core 23 presentsa machined radially inside (first) surface 26 and a radially outside(second) surface 24. The radially inside surface 26 defines a pluralityof radially-outwardly extending slots 28 that are circumferentiallyspaced from one another and define a plurality of teeth 30circumferentially therebetween. One or more electrical conductors 31 arereceived in each of the slots 28 and are collectively configured toselectively create a moving magnetic field which acts upon the rotor 14for providing rotation of the rotor 14 in response to a current beingapplied thereto. As shown in the example embodiment, the electricalconductors 31 may be comprised of one or more axially extendingconductive bars 31. Alternatively, the electrical conductors 31 could becomprised of windings that are wrapped about or otherwise coupled to theteeth 30. At least a portion of one or more of the electrical conductors31 in each of the slots 28 extends radially inwardly from the slot 28substantially into radially alignment with, or past the inside surface26 of the stator 12 such that the electrical conductor 31 at leastpartially defines an outer stator raceway 32. The electrical conductors31 may therefore define the outer stator raceway 32 alone, or incombination with the inside surface 26 of the stator 12. Under thearrangement in which the outer stator raceway 32 is defined by both theelectrical conductors 31 and the inside surface 26 of the stator 12, theouter raceway 32 may be defined by circumferentially alternatingsegments of the electrical conductors 31 and the inside surface 26 ofthe stator 12. The use of the electrical conductors 31 to define theouter raceway 32 allows the electrical conductors 31 to not only providecurrent conduction to drive the rotor 14, but also to mechanicallysupport the stator 12. This eliminates the need for a separate statorbearing sleeve to mechanically support the stator 12, thus providing asimpler and compact assembly and simplifying manufacturing and assemblyof the electric motor 10. The rightmost slot 28 in FIG. 4 illustrates anarrangement in which the electrical conductors 31 extend radiallyinwardly of the stator 12, while the other slots 28 of FIG. 4 illustratearrangements in which the electrical conductors 31 are in substantialalignment with the stator 12. Any combination of the electricalconductors 31/slots 28 shown in FIG. 4A may be used.

With reference to FIGS. 1, 3 and 4 , the rotor 14 is comprised of arotor core 33 and a plurality of magnets 35 positioned about an outersurface of the rotor core 33. As shown in FIG. 3 , the magnets 35 mayeach generally extend axially, and may be arranged in circumferentiallyspaced relationship with one another. A radially outer perimeter 34 ofthe rotor 14 (along the magnets 35) defines an inner rotor raceway 36.The outer and inner raceways 32, 36 are configured to act as a bearingby accommodating relative rotational movement between the stator 12 androtor 14 in the event that the inner and outer raceways 32, 36 contactone another in response to radial movement between the rotor 10 andstator 12. As will be discussed in further detail below, because theelectrical conductors 31 partially define the outer raceway 32, they areconfigured not only to conduct a current to provide rotation of therotate 14, but also to mechanically support the stator 12.

As best shown in FIGS. 4 and 4A, the electrical conductors 31 may becomprised of two or more layers 38, 40, 42 of electrical conductors 31that are stacked on top of one another in the radial direction.According to the example embodiment, the stacked layers 38, 40, 42 ofelectrical conductors 31 include a top layer 38, a middle layer 40 and abottom layer 42, however, more or fewer layers 38, 40, 42 could beutilized without departing from the scope of the subject disclosure. Thestacked layers 38, 40, 42 of electrical conductors 31 are assembled insuch a manner as to provide a tight fit in the slot 28 using any of anumber of techniques such as an interference press fit, thermal shrinkfit, displacement/deformation rolling processes and others. Asillustrated in FIG. 4 , each layer 38, 40, 42 of electrical conductors31 may be comprised of a plurality of conductive bars, however, as shownin FIG. 4A, each layer 38, 40, 42 could alternatively be comprised ofonly a single conductive bar.

The top layer 38 which defines the portion of the outer raceway 32 iscomprised of a lower conductivity and harder material (e.g., copper iron(CuFePCoSn) or copper zinc (CuZn5)) than the layers 40, 42 below it inorder to provide minimal electrical resistance of the overall electricalconductors 31 while also providing a harder surface for the outerraceway 32. On the other hand, the middle and bottom layers 40, 42 arecomprised of a material that has higher conductivity and is softer(e.g., oxygen carrying copper (Cu-ETP) or oxygen-free high conductivitycopper (Cu-OF)) than that of the top layer 38 in order to provide anadequate magnetic field. Copper alloys with very high conductivity aretypically mechanically softer materials, and less than optimal forbearing surfaces. On the other hand, harder copper alloys that are moresuitable for bearing surfaces typically have a lower conductivity whichwould work against motor efficiency if used in a layer beneath the toplayer 38. By using high-conductivity/soft materials andlower-conductivity/hard materials in the right radial locations of theelectrical conductors 31, a hard bearing surface and sufficientconductivity are provided. As illustrated in FIGS. 4 and 4A, thestructure of the stacked layers 38, 40, 42 of electrical conductors 31achieves mechanical stiffness by having the layers 38, 40, 42 ofelectrical conductors 31 arranged with flat surfaces 45 stacked uponeach other with a minimal insulating layer therebetween. Moreparticularly, each of the layers of electrical conductors 38, 40, 42includes at least one substantially planar bottom and/or top surface 45,with the substantially planar surfaces 45 overlying and engaging oneanother in the slot 28.

As further illustrated in FIG. 4 , according to an embodiment, the outerraceway 32 may present a substantially smooth surface in thecircumferential direction. This may be provided by the electricalconductors 31 alone or in combination with the teeth 30. As part of thisarrangement, a polymer coating 47 may extend over the electricalconductors 31 in each of the slots 28 and the first surface of thestator 12 to define the substantially smooth surface. The smooth surfacemay be provided about part of, or an entire circumference of the outerraceway 32.

As further illustrated in FIG. 4 , one or more of the electricalconductors 31 may define a cooling passage 43 which may receive coolantfrom the high or low pressure sources 21, 24 for cooling the electricalconductors 31. Any number of cooling passages 43 may be provided on anynumber of the electrical conductors 31.

The stator laminations 25 are assembled and held with sufficientcompressive forces and sealing to avoid lubricant oil infiltration intothe laminations 25. Techniques/features for providing such compressiveforces and sealing include:

-   -   Overall structures to compress the laminations 25 of the core 23        of the stator 12. For example, a housing may be shrink-fitted        over an outer diameter of the stator 12 and may include end        plates that are pulled together with bolts or other fasteners to        hold the laminations 25 in place.    -   Surface welding/bonding of the laminations 25 of the core 23 of        the stator 12. For example, outside and/or inside diameters of        the stator 12 may be welded to ensure integrity of the stacked        laminations 25 of the stator 12. Additionally, an outside or        inside diameter of the stator 12 may be bonded with a structural        adhesive or molded-on polymer layer to ensure integrity of the        stator 12 and seal the stator 12 against oil introductions.    -   Insulation of the laminations 25 of the stator 12 with        sealing/bonding properties. More particularly, the laminations        25 of the stator 12 may be electrically insulated from one        another with a material such as varnish.

During assembly, after the stacked layers 38, 40, 42 of electricalconductors 31 are positioned inside the slots 28, the outer raceway 32is optionally machined or finished to create a smooth finish of theouter raceway 32 that is suitable for the application of interest. Theinner and outer raceways 36, 32 may include features to improve andmaintain the film of lubricant 18 (e.g. close-tolerance areas, pocketareas, and others). This may include bearing structures such as areknown for hybrid journal bearings. Moreover, the assembled structures ofthe stator 12 can also be used to create bearing surface features alongthe outer raceway 36, such as:

-   -   Bearing hydrodynamic, close clearance regions (see, e.g., close        clearance region 37 in FIG. 4 .)    -   Bearing hydrostatic pocket regions:        -   One or more of the electrical conductors 31 may be located            slightly radially outwardly of the teeth 30 (i.e., the            electrical conductors 31 may be slightly more shallow than            the teeth 30).        -   Edges of the slots 28 may formed by laminations or copper            windings which extend radially inwardly to a greater extent            than the teeth 30 of the stator 12. See, for example, the            perimeter of copper laminations 39 shown in FIG. 4 .        -   As shown in FIG. 2 , drain gutters 41 may be formed along an            inside diameter of the stator 12, and hydrodynamic pockets            43 may be formed along an inside diameter of the electrical            conductors 31.    -   Bearing hydrodynamic regions with compliance to offer        close-clearance relief in high-rpm, high-dynamic-pressure        conditions; and    -   Bearing hydrodynamic regions with compliance to offer load        sharing in shock loading and high acceleration conditions        (create conditions conducive to squeeze film formations). More        particularly, close-clearance bearing hydrodynamic areas where        stiffness of the stator laminations and/or copper electrical        conductors 31 may be reduced or be “compliant” so that in heavy        shock load cases where the rotor weighs heavily on the stator        12, the stator 12 deforms a small amount to increase the area of        rotor 10 and stator 12 that are in contact.

In view of the foregoing, the stacked layers 38, 40, 42 of electricalconductors 31 arranged circumferentially between teeth 30 of the stator12 are arranged in such a manner to:

-   -   Provide stiff, compressive mechanical support to compensate for        loads applied to the outer raceway 26.    -   Provide electrical insulation circumferentially between the        electrical conductors 31 via the teeth 30.    -   Provide thermal conduction to the core 23 of the stator 12 for        cooling purposes.    -   Provide mechanical support for the electrical conductors 31 in        the event that they are subjected to magnetic forces and        mechanical vibrations.    -   Provide in-slot 28 cooling passages 43 as needed (e.g., as shown        in FIG. 4 ).    -   Provide mechanical support for the core 23 of the stator 12 and        electrical conductors 31 under conditions of different thermal        expansion of the laminations of the core 23 and electrical        conductor 31 structures. For example, the tapered shape of the        slots 28 compresses the electrical conductors 31 downwards        toward the radially outside surface 24 of the core 23, which        maintains a diameter of the outer raceway 32.    -   Provide for different materials in lower layers 40, 42 of        electrical conductors 31 which are primarily used to provide        conduction versus the top layer 38 of electrical conductors 31,        which is primarily used as part of the inner raceway 36.

The structure of the stator 12 can also incorporate features to supportother aspects of motor operation, such as:

-   -   Bearing lubricant supply passages 20.    -   Bearing lubricant supply passages 20 with capillary or orifice        regions to restrict lubricant flow.    -   Cooling with oil routed through the stator 12 to the bearing        area through the supply passages 20.    -   Rotor 14/stator 12 proximity sensing with capacitance bridge        measurements.    -   Rotor 14/stator 12 proximity sensing with variable reluctance or        hall-effect magnetic sensing.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings and may be practicedotherwise than as specifically described while within the scope of theappended claims. These antecedent recitations should be interpreted tocover any combination in which the inventive novelty exercises itsutility.

What is claimed is:
 1. An electric motor comprising: an annular statorextending about an axis and presenting a first radial surface; a rotorextending about the axis and rotatable relative to the stator andpresenting a second radial surface defining a rotor raceway disposed inspaced relationship with the first radial surface of the stator todefine a gap therebetween for containing a lubricant; the first radialsurface of the stator defining a plurality of slots in spacedrelationship with one another to define a plurality of spaced teethbetween the slots; at least one electrical conductor disposed in each ofthe slots and configured to selectively create a moving magnetic fieldfor acting upon the rotor for providing rotational movement of the rotorin response to a current being applied to the at least one electricalconductor; and a portion of the at least one electrical conductor ineach of the slots extending substantially into radial alignment with, orpast the first radial surface of the stator to at least partially definea stator raceway of the stator for engaging the rotor raceway of therotor during relative movement between the rotor and the stator tofunction as a bearing while also creating the moving magnetic field. 2.The electric motor as set forth in claim 1, wherein the at least oneelectrical conductor in each of the slots includes a plurality ofelectrical conductors in each of the slots, and wherein the plurality ofelectrical conductors in each of the slots includes at least a firstelectrical conductor radially stacked over a second electricalconductor, and wherein the first electrical conductor is made of aharder and less conductive material than the second electricalconductor.
 3. The electric motor as set forth in claim 2, wherein thefirst and second electrical conductors in each of the slots are fittedin the slot using at least one of an interference press fit, thermalshrink fit, and a displacement/deformation rolling process in order toprovide a tight fit of the first and second electrical conductors in theslot.
 4. The electric motor as set forth in claim 2, wherein each of thefirst and second electrical conductors of each of the slots defines atleast one substantially planar surface, and wherein the substantiallyplanar surfaces of the first and second layers of electrical conductorsoverly and engage one another in the slot in order to provide mechanicalstiffness and to minimize insulation between the first and second layersof electrical conductors.
 5. The electric motor as set forth in claim 1,wherein the at least one electrical conductor in each of the slots is anaxially extending conductive bar.
 6. The electric motor as set forth inclaim 1 wherein the at least one electrical conductor in each of theslots is comprised of a plurality of windings.
 7. The electric motor asset forth in claim 1, wherein the at least one electrical conductor ineach of the slots extends radially inwardly past the first radialsurface of the stator.
 8. The electric motor as set forth in claim 1,wherein the at least one electrical conductor in each of the slotsextends into radial alignment with the first surface of the stator suchthat the stator raceway is defined by circumferentially alternatingsegments of the electrical conductors and the first surface of thestator.
 9. The electric motor as set forth in claim 1, wherein thestator raceway presents a substantially smooth surface in thecircumferential direction.
 10. The electric motor as set forth in claim9, wherein a polymer coating extends over the at least one electricalconductor in each of the slots and the first surface of the stator todefine the substantially smooth surface of the outer raceway.
 11. Theelectric motor as set forth in claim 1, wherein the stator defines atleast one passageway in fluid communication with the gap for passing alubricant into the gap.
 12. The electric motor as set forth in claim 1,wherein a bearing sleeve is not located radially in the gap between thestator and the rotor.